Obesity is increasingly recognized as a major public health problem that is showing an alarming rise in prevalence in young people. While environmental factors, such as high-fat diets and lack of exercise, account for much of this rise, genetic differences may make some people more prone to obesity than others, even when diet and activity levels are similar among them. Obesity often has its genesis during childhood and, especially, adolescence, when differences among individuals in body fat amount and distribution tend to develop during puberty. It is thus important to understand the factors that affect growth, development, and body composition during this period. We will investigate the genetic factors that influence growth and body fat deposition during adolescence by using data and biological samples previously collected during Project HeartBeat!, a longitudinal study of cardiovascular disease risk factor development during childhood and adolescence. In two Texas communities, schoolchildren from 8-18 years of age were measured up to 3 times annually over a 4-year period, encompassing the ages when puberty normally occurs and adult body habitus usually develops. Subjects were enrolled at 8, 11, or 14 years of age to establish 3 separate cohorts that would overlap in age as the study progressed and permit construction of a synthetic cohort encompassing the full 10-year age range of the participants. The sample included 136 African Americans (70 females) and 506 non-Hispanic whites (250 females), with a mean of 8.6 examinations per subject. In each individual, we will genotype multiple single-nucleotide polymorphisms (SNPs) in 80 genes from hormonal systems important in growth and development, emphasizing genes known or suspected to affect body size and body fat distribution. In each gene, all promoter region and exonic SNPs, together with haplotype-tagging SNPs identified in public databases by 3 different algorithms, will be typed. A 3-stage algorithm will be used to identify a subset of SNPs in which multilevel mixed models will be used to analyze the associations of both individual variants and multilocus haplotypes with variation in longitudinal growth curves for traits related to obesity and body fat distribution, such as body mass index, % body fat, and various skinfolds. By targeting genes known to be involved in the development of body size and composition, we will significantly increase our understanding of the genetic factors that contribute to interindividual variation in growth and body fat distribution. Our analyses may also help identify genetic variants that may predispose some individuals toward obesity.